Newer convertible vehicles are often equipped with a movable convertible top, which can be automatically moved for example from an open to a closed position or vice versa with the push of a button. The movement of the convertible top is usually effected by a hydraulic drive, which in turn drives a convertible top mechanism, which includes a convertible top linkage, wherein the convertible top linkage may be a carrying device for a textile roof as well as a so-called hard-top folding roof with mainly rigid roof elements, and comprises, where applicable, a cover for a convertible top compartment as well as all elements that are being moved in the process.
Since problems in the process of the convertible top motion such as a decelerated movement or jamming of the convertible top can be hints that an object or a person's body part might be caught in the convertible top linkage, and this type of obstruction situation requires an immediate reaction to avoid injury, it is common knowledge to provide a detection device to recognize an interference into the range of motion of the convertible top mechanism.
European Patent Application 0 943 473 A2 describes a motor vehicle with a convertible top that can be moved using a drive with a convertible top control, wherein sensors that are in particular designed as cameras are provided to recognize the position of the occupants in a vehicle interior. The sensors, which are attached above the occupants, monitor a safety area between the occupants and the convertible top in addition to the position of the occupants in their seats and are connected to a convertible top control. As soon as the convertible top control recognizes that the occupants do not stay out of a safety zone below the convertible top and therefore injuries to the occupants caused by the moving convertible top can not be ruled out, the convertible top drive is stopped.
The disadvantage of the sensors provided in EP 0 943 473 A2, which can be cameras, infrared sensors or ultrasonic sensors is that they are often prone to errors in regard to their signals and, in the event that optical sensors are used, that they can not monitor blind spots.
German Patent Application 197 23 974 A1 also describes a method to prevent foreign objects being caught in an opening that is to be closed using a power-operated device, which operates with an opto-electronics sensor system. When a foreign object is caught in an opening that is to be closed, the power-operated device is switched off or switched to reverse mode using a detector beam. The direction of the detector beam is continuously changed in the process, so that the detector beam moves over the area of the edge of the opening that is to be closed.
However, this type of obstruction sensor can only be implemented with significant effort for the movable convertible top of a convertible and does not offer any protection against injuries in the event of errors or system failure.
Practice has shown that a detection of obstructions is possible with adequate accuracy with the aid of a capacitive sensor device.
This type of obstruction sensor with a capacitive sensor system is described in German Patent Application DE 198 36 056 A1, wherein the device that is being used to detect the obstructions, in particular when automatically closing convertible tops, vehicle windows or the like includes a capacitive sensor device, which consists of an electroconductive transmitter surface on one side, and an electroconductive sensor wire and at least one metal surface that is mainly potential-free on the other side of an insulator. The transmitter surface and the sensor wire are connected to an electronic analysis circuit.
The disadvantage of these types of obstruction protection devices operating with a capacitive sensor system is the same as for those of other obstruction protection devices using pressure sensors that are known from practical applications: they react very late in the event of an obstruction situation, in the case of pressure sensors not until the object that interferes with the movement has made contact.